A characteristic of bicycles having this type of brake operator for the driven wheel is that an application of the brake sufficient to lock the driven wheel will also lock the chain wheel which is in driving connection with the driven wheel through the chain. It is therefore necessary to make provision for sufficient forward movement of the pedal crankshaft independent of the chain wheel to permit release of the brake. This problem has been recognized in the art, and proposals have been made to permit the necessary lost motion between the chain wheel and the pedal crankshaft. Examples of such arrangements are to be found in U.S. Pat. Nos. 3,888,334 (Mack), 4,134,481 (Calderazzo), 4,260,044 (Foster) (this is only exemplary of several Foster patents showing this feature), Swiss Pat. No. 205,840 (Montanus), and in my own U.S. Pat. No. 4,462,488. A potential problem common to all of these arrangements is that whilst they provide the desired lost motion, the connection between the chain wheel and the pedal crank is such that the lost motion may be accompanied by wobbling or unsteadiness of the chain wheel, particularly as wear takes place. In most cases, the centre of the chain wheel is supported directly on the pedal crank, so that any lateral free play at the point of support will result in a much greater "wobble" of the wheel at its perimeter, or is supported by spaced pin and slot connections to a plate or spider fast to the crankshaft. Whilst the latter arrangement reduces amplification of wobble in the system, it is difficult to provide a pin and slot connection which is free of play in an unwanted direction, and the bearing surfaces available are very restricted. A-further problem in many arrangements lies in avoiding jerky operation as the lost motion between the crank and the chain wheel is taken up during normal operation of the bicycle. In my U.S. Pat. No. 4,583,422 I describe an arrangement for mounting a chain wheel on a pedal crank which addresses the "wobble" problem, whilst a solution to the problem of jerky operation is disclosed in my U.S. Pat. No. 4,462,488 already mentioned above, utilizing a suitably calibrated spring to connect the parts.